Radio transmitter



May 22, 1945. E. GREEN ET AL RADIO TRANSMITTER 2 Sheets-Sheet 1 Filed June 22, 1944 firm/P1149 May 22, 1945.

E. GREEN ET AL 2,376,480

RADIO TRANSMITTER Filed June 22, 1944 2 Sheets-Sheet 2 AAAAAAA VVVVV IN V EN T 0R5 Ernest fireen ergies for the two radio Fatented May 22, 119% was ' w TRANSTER Ernest Green, Chelmsiord, and Newsome Henry Clough, Brentwood, England, assignors to Redio Corporation oi America, a

Delaware corporation of Application Jimmie 22, 1944, Serial No. 541,550 En Great Britain April 15, 1943 Claims.

This invention relates to radio-transmitters and particularly, though not exclusively, to equisignal beacon radio-transmitters.

In a known kind of equisignal beacon radiotransmitter, it is required to transmit two overeffected without interfering with the beam of constant phase position.

The use of single high-frequency stage, coupled to a single modulator, for supplying the two enbeams has much to recommend it from the point of view of simplicity.

The phase of the periodically varied energy can be reversed by means or a key cooperating with a transformer having a centre tapped secondary winding. The voltages at the two ends of the secondary winding are, relatively to the centre point, in opposite phase to each other. The said centre point may then be connected to one terminal of the load to which the periodically varied energy is to be applied, and the two ends may be connected, in alternation, by means of a keying contact, to the other terminal of the said load.

However, during the time that the keying contact is efiecting its switching operations, the loading of the final stage of the transmitter will be varied, and this may produce violent fluctuations in the high-tension voltage for this stage. These violent fluctuations in high-tension voltage will produce corresponding fluctuations in the highfrequency energy supplied to the load circuit to which the energy of invariable phase position is applied. In addition, there will be fluctuations due to the regulation of the high-frequency stage itself. These fluctuations produce violent keyclicks in the receiver and thus seriously reduce the usefulness of the system.

It is the object or this invention to overcome the fluctuations produced in the manner set out above.

According to' this invention, a radio-transmitter includes a high-frequency stage having an output circuit for supplying high-frequency energy to an associated loadcircuit, means for keying said load circuit, a main modulating valve said stages being connected in series with each other across a high tension source of energy with the high-frequency stage connected between the stage. the two sion source of energy.

cathode of said main modulating stage and the negative terminal or said source, and means for applying modulating potentials between the control grid of said main modulating stage and said negative terminal.

The means for applying modulating potentials may include a rectifier arrangement for providing a controlling voltage such level of the high-frequency energy in accordance with the amplitude of the modulating signals.

The keyed radio-transmitter may include a rectifier for rectifying a portion of the keyed highfreouency energy supplied to said load circuit to provide a direct-current bias, and means for applying said bias to said means for applying modulating potentials so as to control the high-tension current supplied to said high-frequency stage and to maintain the high-frequency energy in said output circuit substantially constant in spite of fluctuations in the energy supplied to said load circuit as a resultof the keying operation,

The radio-transmitter may be organized as an equisignai transmitter, two load circuits being associated with said output said load circuits being keyed, and the keying be ing such as to produce variations of the phase of the high frequency energy in said keyed load circuit relatively to that in the other load circuit, which is maintained at a constant phase position.

There ma be two high frequency stages each in series with the said main modulating stage and in parallel with each other, and each supplying high-frequency energy to a difierent one of said load circuits.

There may be two high frequency stages each in series with a separate main modulating stage and supplied in common from a single high-ten- Generally, in this case, it will be unnecessary to apply said bias, obtained by rectification of said portion of high-frequency energy, to said means for applying modulating v potentials.

Where the invention is applied to an equisignal beam transmitter in which there is provided two load circuits, and means for coupling the said output circuit to both said load circuits so as to supply thereto modulated high frequency energy of variable and of invariable phase position, and it is desired to key the high-trequency energy in said output circuit, a keying device may be provided for keying the low-frequency modulating tone at a low-level stage.

The invention is illustrated in the accompanying drawings, Figure 1 illustrating one embodiment, and Figure as to control the rcuit, only one of I 2 illustrating those parts which Vl is connected between the positive and negative terminals of a source of anode current (not shown, but indicated by the references +HTI and HTI a load resistor RI being included on the anode side of the said valve.

The anode of audio amplifier valve VI is coupled, hrough a coupling a source of potential +HT4, HT4. other ends are also, each separately, coupled through capacitors C2 and C3 to the positive end of the voltage divider R4. Tapping points on these resistors R2 and R3 are connected to the grids of a second and a third valve, respectively V2 and V3.

The cathode of the valve V2 is connected to the cathode of a valve V3. The anode/cathode space, and the cathode/anode space of valves source of anode current (not shown but indicated by the references +HT2 and HT2) load resistors, respectively R and R6, being included on the anode side of each of these valves. A third source +HT3, -HT3 of anode current is connected across valve V3 and its anode loadresistor R6, with its negative terminal connected to the cathode of the valve. v

The positive end of the said voltage dividing resistor R4 is connected to the anode end of the anode load-resistor R6 and valve V3.

A condenser-shunted resistor combination R1, C1 is connected across the anode/cathode space of valve V3, and the grid of this valve connected to a tapping point on resistor R3. The two re-' sistors R2 and R3 thus su ve to apply bias to the grids of valves V2 and V3 respectively.

The anode of valve V2 is connected to the grid of a main modulating valve V4, whose anode is connected to the positive terminal +HT2 of the said second source of anode current.

The high-frequency stage is constituted as a high-frequency amplifier, and includes two radiofrequency valves V5 and V6 having their caththe load circuit (LdZ) to odes connected together and to the common earthed negative terminals I HTI, first-mentioned and second-mentioned sources of anode current and positive terminal +HT3 of the third source. A high-frequency tuned circuit HFIP, comprising inductor L2 and capacitor C5 is connected in push-pull to the grids of thesetwo radio-frequency valves, V5 and V6. The high-frequency tuned circuit is coupled to inductor Ll of the input circuit. A high-frequency tuned output circuit I-IF'OP is connected in push-pull to the anodes of the two radio-frequency valves V5 and V6, and the anode of each is coupled, by means of a capacitor C", to the transformers, connected in nected to the midpoint of the primary winding L8 of the said first transformer. Anode current for the two high-frequency valves V5 and V8 is supplied and controlled through and by this main modulating valve V4.

The high-frequency tuned output circuit also includes, as part of its inductance the seriesconnected primary windings L3 and L4 of two parallel with the primary winding L8 of the said first transformer.

The secondary windings L5 and L8 01 the said two transformers are connected in series, and their point of juncture is connected to one of the terminals of the load circuit (not shown but indicated by reference Ld2), to which energy of variable phase-position is to be applied. The connections of these two transformers will be tion.

The free ends of the secondary windings L5 and L6 of the said two transformers are coupled by way of tuning capacitors CH and CI! to the alternative stationary contacts KI and K2 of a keying device (key or relay contact), whose moving contact K3 is connected to the other terminal of the load circuit (M2), to which energy of variable phase-position is to be applied.

With this arrangement, in which modulation is efiected by means of a cathode follower modulator, large changes in the impedance of the load circuit as a whole, resulting from the keying of which high-frequency of variable phase position changes in the load, particularly during the period of time when the moving contact W3 of the keying device is out of its alternative stationary contacts Kl or K2, there will be very little change in the high-tension voltage applied to the of the high-rrequency circuit (Ldl) to which invariable phase posilittle change in the level energy applied to the load high-frequency energy of tion is applied.

When a rectifier is employed for rectifying a portion of the high-frequency energy applied to that load circuit to which high-frequency ener y of variable phas'e described circuit arrangement is modified by the additions illustrated in Figure 2,-in the following manner.

The grid of the second valve V2, being directly connected to the tapping point on resistor R2, and thence through said coupling capacitor CI to the anode of said coupled thereto through a resistor R8. The said coupling capacitor Cl and resistor R8 are thus in series between the said grid and the said anode.

The moving contact K3 or the said keying device, instead of being directly connected to the said other terminal of the load circuit Ld2, is connected thereto through the primary winding 9. whole, and thus but position is applied, the above first valve, is I L9 of a coupling transformer. The said coupling transformer is provided with a tuned secondary winding Lid. and across winding are connected a rectifier Ti and the load resistor R8 already mentioned, in series. A smoothing capacitor me is connected across resister as. The sense of connection of the rectiher is such as to tend to make negative that end of resistor Rt which is connected to the grid of valve V2.

In operation, when high-frequency energy is applied to the load circuit L412, to which energy of variable phase-position is to be applied, a direct voltage is developed across resistor R3, such as to increase the negative bias on the of valve V2, so that the current through this valve and through its anode resistor R is reduced, and its anode potential becomes more positive. C- quently, the bias on the grid of the main modulator valve V 3 also goes more positive, as does also the potential of the cathode of this in modulator valve, so that the direct voltage applied to the high-frequency stage is raised, as is required.

Keying of the whole of the high-frequency stage may be edected by means of a keying device Kt, connected between the grid of the first audio amplifier valve Vi in the modulator stage and the source of modulation frequency G.

The invention may be modified. Thus. instead of mechanical keying devices, other lmown keying systems, such as thermionic switching devices may be used. Moreover, the invention can be applied to a transmitter in which two high-drequency stages are used. Referring to Figure 3, the high frequency valves V5 and vs are connected to supply only the load Ldl, A second pair of high frequency valves, vice and Vito, are connected in similar manner to supply only the load M2. The main modulator valve V6 is connected between the anode supply terminal +H'l2 and both pairs of high frequency valves. so as to modulate the energy applied to both loads, as in the system of Figure i.

In the modification illustrated in Figure 4,-sep arate high frequency valves will and Vice are provided for the load lids, as in, the system of Figure 3. However, the main modulator value V6 is connected to modulate only the valves Vt and Vi. a separate main modulator valve Ville being provided for valves with and WM. Both modulator valves Vt and Vis t are connected to the amplifier valve V 2, as the valve W3 is connected in the system of Figure l. The biasingsystem described in connection with Figure 2 may he provided for the valve V2. The operation of the system of Figure 4 is substantially identical with that of the system of Figure 2.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim ls:-

1. A radio-transmitter including a high-frequency stage having an output circuit forsupplying high-frequency circuit, means for keying said load circuit, a main modulating valve stage, the'two said stages being connected in series with each other across a high tension source of energy with the high-frequency stage connected between the cathode of said main modulating stage and the negative terminal of said source, and means for applying modulatlng potentials between the controlgrldof said main modulating stage and said negative terminal.

2. A transmitter as claimed in claim 1, wherein this tuned secondary the means for applying modulating potentials includes a rectifier arrangement for providing a controlling voltage to control the level of the high-frequency energy in accordance with the amplitude of the modulating signals.

.3. A radio transmitter including a high frequency stage having an output circuit for suppl ing high frequency energy to an associated load circuit, means for keying said load circuit, a main modulatingyalve stage, the two of said stages being connected in series with each other across a high tension source of energy with the high frequency stage connected between the cathode of said main modulating stage and the negative terminal of said source, rectifier means arranged to rectify a portion of keyed high frequency energy supplied to said load circuit so as to provide a D.-C. bias, means for applying modulation potential between the control grid of said main modulating 'stage and said negative terminal, and means for applying said D.-C. bias to said modulating means to control the current supplied to said high frequency stage and to maintain the high frequency energy in said output circuit substantially constant independently of fluctuations in the energy supplied to said load circuit as a result of said keying operation.

d. In an equlsignal range transmitter, a high frequency stage having .an output circuit for supplying high frequency energy to two associated load circuits, means for keying one of said load circuits so as to produce variations in the phase of the high frequency energy in said keyed load circuit relatively to that in said other load circuit, a main modulating valve stage, the two said stages being connected in series with each other across a high tension source of energy w th the high frequency stage connected between the cathode of said main modulating stage and the negative terminals of said source, and means for applying modulating potentials between the control grid of said main modulating stage and said negative terminal, said means including a recti fier arrangedto rectify a portion of the keyed energy to an associated load high frequency energy to provide a D.-C. bias for controlling the current suppliedito said high tirequency stage.

5. A transmitter as claimed in claim 4, but wherein there are two high frequency stages each in series with the said main modulating stage and in parallel supplying high-frequency energy to a difierent one of said load circuits.

6. A transmitter as claimed in claim 4, wherein there are two high frequency stages each in series with a separate main modulating stage and supplied in common from a single high-tension source of ener y.

'7. A transmitter as claimed in claim 4, including two high-frequency stages each in series with a separate main modulating stage and supplied in'coznmon from a, single high-tensionsource of energy, and wherein saidbias obtained by rectification of said high-frequency energy is applied to both said modulating means.

8. A transmitter as claimed in claim a, including a keying device provided for keying the lowfrequency modulating otentials at a. low-level stage.

9. In an soul-signal beam radio-transmitter, a modulated high-frequency stage and two loadcircuits coupled thereto in such manner that the ener applied tov one load circuit has a predetermined phase relationship to the energy applied to the other load circuit and is adapted to be with each Other, and each circuit and its anode periodically reversed, said high irequency stage including a modulator valve and two high-frequency valves having a tuned high-frequency input circuit connected in push-pull to the controlgrids thereof and a tuned high-frequency output circuit connected in push-pull to the anodes thereof, the modulator valve having its cathode connected to the mid-point of the tuned output energy applied to one load circuit has a predetermined phase relationship to the energy applied to the other load circuit and is adapted to be periodically reversed, said high frequency stage including a modulator valve and two high-frequency valves having a tuned high-frequency input circuit connected in push-pull to the controlgrids thereof and a tuned high-frequency output circuit connected in push-pull to the anodes thereof, the modulator valve having its cathode connected to the mid-point of the tuned output to the positive terminal of a source of high-tension energy and the high-frequency valves having their cathodes connected in common to the negative terminal of said source, wherein means is connected between the grid of said modulator valve and the cathodes of said high-frequency valves so as to apply modulating potentials to said control grid, said means including at least one further valve, an anode resistor connected between the anode of said further valve and said cathodes of said high frequency valves, and a circuit element connected between the cathodeof said further valve and the positive terminal of said source, said circuit element comprising a valve and anode resistor in series, the

cathodes of these last two valves being connected together, the control grid of the modulator valve being connected to the anode of the valve in said circuit element, and a source of anode current for said further valve being connected across the anode/cathode space thereof. v

11. A transmitter as claimed in claim 10, including an audio amplifier valve having connected across its anode/cathode space two resistors in parallel with each other and in series with the anode resistor of said further valve, the grids oi the said further valve and 01' the valve in said circuit element being connected to tapping points on the last mentioned two resistors respectively.

12. A transmitter as claimed in claim- 10, including an audio amplifier valve having con-' nected across its anode/cathode space two resistors in parallel with each other and in series with the anode resistor of said further valve, the grids of the said further valve and of the valve in said the grid of the circuit element being connected to tapping points on the last mentioned two resistors respectively, and a source of bias potehtial and means including said two last mentioned resistors for applying biassing potential therefrom to the grids of said further valve and of the valve in said circuit element.

13. A transmitter as claimed in claim 10, including an audio amplifier valve having connected across its anode/cathode space two resistors in parallel with each other and in series with the anode resistor of said further valve, the grids of the said i'urther valve and of the valve in said circuit element being connected to tapping points on the last mentioned two resistors respectively, a source of bias potential and means including said two last mentioned resistors for applying biassing potential therefrom to the grids of said 7 further valve and 01 the valve in said circuit control-voltage resistor between valve in said circuit element and the resistor of said last-mentioned two resistors. to a tapping point on which said grid is connected, and means for producing across said 'control-voltage resistor a potential derived from the energy applied to said one load circuit, in such sense as to increase the bias on the grid 01 said further valve thereby to increase the potential applied to the anode of said modulator valve and thus to increase the high-frequency output of the system as a whole.

14. A transmitter as claimed in claim 10, wherein said tuned high-frequency output circuit includes two inductors connected in parallel with each other, each or which is inductively coupled to a different one of said load circuits, that inductor which is coupled to said one load circuit comprising the series connected primary windings of two transformers whose secondary windings are connected in series, one terminal of the said one load circuit being connected to th point of juncture of said two secondary windings and the other terminal of said one load circuit being element, and a connected alternately, in keying rhythm to the two free ends of said secondary windings.

15. A transmitter as claimed in claim 10,

wherein said tuned high-frequency output circuit includes two inductors with each other, each of which is inductively coupled to a diil'erent one of said load circuits, that inductor which is coupled to said one load connected in parallel circuit comprising the series connected primary windings of two transformers whose secondary windings are connected in series, one terminal of i the said one load circuit being connected to the point of juncture of said two secondary windings and the other terminal of said one load circuit being connected alternately, in keying rhythm to the two free ends of said secondary windings, the cathode of the modulator valve being connected to the mid-point of the tuned output circuit by a connection to the mid-point of either of said inductors.

ERNEST GREEN.

NEWSOME HENRY QIDUGH. 

